Part II: Rules of Air Warfare#Chapter V: On Military Authority over enemy and neutral aircraft and persons on board. - Art. 37.

Art. 37. The members of the crew of a neutral aircraft who have been arrested by a belligerent shall be released unconditionally if they are neutral subjects and if they are not in the enemy's service. If they are enemy subjects or if they are in the enemy's service, they may be made prisoners of war.

The passengers must be released unless they are in the enemy's service or enemy subjects fit for military service, in which case they may be made prisoners of war.

The release may, in all cases, be postponed if the military interests of the belligerent require it.

The belligerent may retain as a prisoner of war every member of the crew or every passenger whose conduct during the flight at the end of which he has been arrested, was of a special active assistance to the enemy.